Interpretive Summary: Stillbirth, preweaning mortality and failure to return to estrus after weaning are all reproductive problems that reduce the efficiency of pork production. Essential fatty acids and zinc participate in a variety of physiological pathways that could influence all three of these reproductive traits. The effect of adding essential fatty acids (Gromega®) or zinc sulfate to female pig diets during late pregnancy on the farrowing process, stillbirth rates, brain development, preweaning mortality, various metabolic parameters during lactation, and post weaning return to estrus was determined. Zinc decreased stillbirth and Gromega® increased stillbirth rate when farrowing was prolonged, and zinc treatment reduced stillbirth rates in low birth weight piglets. Combined Gromega® and zinc treatment increased the amount of high molecular weight myelin basic protein (a primary component of myelin, which plays a role in coordination and reflexes) from the brain stem of piglets. No effect of either treatment was found for preweaning mortality. Gromega® supplementation increased back fat in pregnant pigs at the end of gestation, but this effect was lost at weaning, and no differences in return to estrus after weaning was found. These results suggest that zinc supplementation could be beneficial in reducing stillbirth rate in piglets, which would increase the efficiency of pig production.

Technical Abstract:
Omega fatty acids and zinc contribute to physiological pathways that could affect the farrowing process, stillbirth, preweaning mortality and postweaning return to estrus. To determine effects of omega fatty acids and zinc on these reproductive traits, gilts were mated and fed either a control diet, a diet supplemented with 1.09% Gromega®, a diet supplemented with 0.07% zinc sulfate or a diet supplemented with both Gromega® and zinc sulfate, from day 80 of gestation until farrowing. Farrowings were video recorded to obtain birth intervals for each piglet, and the number of live and stillborn piglets was recorded. On day 1 after farrowing, piglets were weighed, and the smallest piglet in each litter was sacrificed. A blood sample was collected to measure the immunoglobulin immunocrit ratio and brain, cerebellum, brain stem, full and empty stomach (to calculate stomach content weight) and heart weights were recorded. Because myelination of specific brain regions may affect preweaning mortality, Brain stem, cerebellum and spinal cord tissues were measured for content of myelin basic proteins and myelin lipids. For remaining piglets, survival to weaning and weaning weights were recorded. Results indicated a weak positive correlation (r = 0.23, P < 0.05) between immunocrit values and brain stem high molecular weight myelin basic protein. There was also a Gromega® by zinc supplementation interaction (P < 0.05) on brain stem high molecular weight myelin basic protein in which the combined treatment was greater than the control or each supplement alone. Zinc treatment decreased stillbirth rate during prolonged farrowing and subsequent preweaning survival of low birth weight piglets. Gromega® increased overall stillbirth rate and increased the stillbirth rate during prolonged farrowing. There were no relationships between myelin measurements and preweaning survival.